In the petroleum industry, the apparatus and machinery used to drill wells is commonly known as a drilling rig or a rig. On these rigs are means of rotating the drill pipe, the most popular and successful of which is a device known as a top drive system. The popularity and proliferation of top drive systems within the oilfield has greatly enhanced the capability of the industry's drillers and operators to handle drill pipe operations in safe and beneficial manners.
One such operation is “back reaming” wherein the operator hoists a drill pipe out of a borehole while simultaneous pumping drilling mud and rotating the drill pipe, thus avoiding the build-up of frictional forces between the drill pipe and the borehole that may lead to the drill pipe being jammed in the borehole. Until recently this back-reaming process has been done either completely manually or has involved the use of complicated controls within the hoisting equipment.
For example, in the manual process, the operator engages a hoisting means by engaging a clutch and then manually manipulating a hoisting throttle, either a hand or foot throttle, to slowly and carefully hoist the drill pipe out of the borehole. However, during this operation, the driller must simultaneously monitor the hookload, and the rotating torque or standpipe pressure (if using a downhole mud motor) for indications that the pipe is in danger of jamming in a lateral direction or a rotational direction, respectively.
Alternatively, in another process, the operator may be required to operate a control system that is connected to the hoisting means. In such a system, upon a command from the operator, the control system activates the hoisting means to slowly hoist the pipe out of the borehole. However, the driller must still monitor the hookload, the rotating torque and/or the standpipe pressure for indications of that the drill pipe may be in danger of jamming in the borehole.
In addition, a problem with both of these processes is that many hoisting systems cannot tolerate holding a drill pipe without movement for an extended period of time, a situation that can occur when a drill pipe does jam in the borehole. Thus, each of these processes relies on the operator's judgment to avoid equipment damage. Accordingly, a need exists for an improved control system that allows for greater control of the back reaming process while reducing operator burden.